There's a lot a truth in what you say. However there is no denying that under any and all circumstances, the Rams oline was somewhere between not good and really bad.
What I suspect is that while we might be deficient in a couple of spots (particularly at Center), I also have NEVER seen an olineman progress under Fisher.....at least not as a Ram. In fact, not one single FA or draft pick on the offense has ever progressed to anything beyond a journeyman under Fisher.
So, I think it is self evident that while we'll need an infusion of players at some spots on the Offense, that the cupboard isn't entirely bare. The Offense has been a product of terrible HC leadership, terrible OC coaching, questionable schemes, injuries particularly during the Bradford era, and marginal player selection.
Player wise it all starts with the QB. But coaching wise it all starts with the HC.
I'm hoping that this new offensive minded HC with the proven QB developers and coaches in high flying offenses will turn this garbage barge.